The present invention relates to an implantable drainage device for the treatment of hydrocephalus. More specifically, the invention relates to an implantable three stage valve providing constant pressure or constant flow characteristics depending on the fluid pressure differential applied across the valve.
Hydrocephalus is a condition rendering the body unable to relieve itself of excess cerebrospinal fluid (CSF) collected in the ventricles of the brain. Excess CSF within the ventricular spaces results in an increase in both epidural and intradural pressures, causing a number of adverse physiological effects including compression of brain tissue, impairment of blood flow in the brain tissue and impairment of the brain's normal metabolism. The treatment of a hydrocephalic condition typically requires relieving the abnormally high intracranial pressure. Various types of valves are available to control the drainage of an excess of CSF from within the ventricles of the brain. Such valves typically drain the excess CSF to a suitable area in the body such as the peritoneal cavity, for example.
Simple pressure regulator valves or check valves are known, and typically are constructed to open and allow the drainage of fluid when the differential pressure between upstream and downstream chamber reaches a certain threshold, preventing the differential pressure from exceeding the threshold. Such simple valves do not compensate for normal differences in the differential pressure between CSF ventricular pressure and pressure in the discharge line, creating the possibility that a valve might open in response to such normal variations and possibly resulting in hyperdrainage of the ventricular spaces. For example, when a patient stands after lying in a recumbent position, the differential pressure will normally increase by reason of the resulting increased height of the fluid column between the patient's head and the selected drainage location within the abdomen, for example. While an increase in differential pressure under those conditions is normal, a check valve might respond by opening and thereby allowing undesired hyperdrainage of the ventricular spaces which, in turn, may result in a potentially serious brain hematoma.
Other types of valves, such as three stage valves, are available in which a flexible diaphragm is mounted within a housing to separate upstream and downstream chambers, and allowing fluid to flow between the chambers through a flow orifice within the diaphragm. In these types of valves, the diaphragm is subjected to the differential pressure between the upstream and downstream chambers and flexes in response to changes in pressure while the orifice interacts with a machined rod passing therethrough. Such a valve is described in U.S. Pat. No. 4,776,839 and No. 4,781,672, for example. When the diaphragm is deformed in response to increasing pressure differentials, the rod increasingly restricts the flow of fluid through the orifice, thereby regulating CSF flow over a range of pressures.
Such types of valves function as flow regulators, operating over a pressure range in which the flow of CSF remains substantially constant. These three stage valves are usually adjustable so that a lower pressure threshold or popping pressure can be preset by providing an adjustable seat against which the rim of the orifice will bear as long as the differential pressure is less than a certain threshold value. Additionally, the maximum tolerable differential pressure within such valves has a predetermined value which is met when the diaphragm experiences its maximum deformation, leaving the entire surface area of the orifice available for the flow of fluid therethrough. While performing satisfactorily, prior art three stage values have required the use of a certain machined parts such as the aforementioned stem or rod to regulate CSF flow. These parts are difficult to manufacture and, once installed in a valve, may also require complex adjustment.
The present invention overcomes these drawbacks by providing a three stage CSF valve having the desired differential pressure/flow characteristics as prior art three stage valves but which is easier and more economical to manufacture and which can be supplied in any of several embodiments. To this end, the invention provides an implantable drainage device for the treatment of hydrocephalus. The invention is embodied in a device which essentially combines three separate valves with distinct functions, the combination of which makes it possible to obtain the desired functions of a three stage valve.
More specifically, the drainage device of the invention combines at least two pressure regulation valves and a flow regulation valve. The first pressure regulation valve of the device is preset to open at a predetermined first or threshold pressure. A flow regulation valve is positioned in series with the first pressure regulation valve to regulate the CSF flow through the device, maintaining a constant flow rate over a range of differential pressures, up to a predetermined cut-off pressure. At the cut-off pressure, a second pressure regulation valve, in parallel with the flow regulation valve, opens to allow drainage at increased flow rates.
By separating the three pressure/flow functions through a combination of three different valves, the manufacture and adjustment of the drainage device of the invention is greatly simplified. Preferably, the first pressure regulation valve will be in series with an assembly of the other two valves which are arranged, most preferably, with the flow regulation valve in parallel with the second pressure regulation valve. Since the closing threshold pressure, or blow-out pressure, must be at least equal to the opening differential pressure for the second pressure regulation valve, it is preferable to provide the flow regulation valve in parallel with the second pressure regulation valve alone. Alternatively, the second pressure regulation valve can be arranged in parallel with an assembly of the other valves wherein the first pressure regulation valve is in series with the flow regulation valve.
In one embodiment of the invention, the flow regulation valve is provided with a flexible diaphragm, mounted within a single biocompatible housing and defining an upstream chamber and a downstream chamber therein. The diaphragm is provided with a central fluid flow orifice therethrough for CSF communication between the upstream and downstream chambers. The orifice is defined by upstream and downstream annular seals surrounding the orifice on the upstream and downstream sides of the diaphragm. An upstream seat is provided in the upstream chamber and opposing the upstream seal around the orifice. Below a minimum or popping pressure, the upstream seat and upstream seal coact to form a flow restricting seal to prevent CSF flow through the orifice.
In operation, differential pressures between the upstream chamber and the downstream chamber and above the popping pressure will bend or flex the diaphragm, pushing its downstream annular seal toward an opposing seat in the downstream chamber. As greater pressure is exerted against the diaphragm, the passage through which CSF flows between the annular seal and the seat in the downstream chamber becomes progressively smaller. Because of the increase in the differential pressure, however, the velocity of the fluid at the passage will increase so that the CSF flow rate remains substantially constant over a range of pressures between the aforementioned popping pressure and a second threshold pressure at which the diaphragm presses its downstream seal against the downstream seat, forming a flow-restricting seal and preventing substantial CSF flow through the outflow port in the downstream chamber. The annular downstream seal and/or the downstream seat preferably include means to allow a slight leakage of CSF, permitting slight drainage of the contact areas between the downstream seal and the downstream seat and preventing proteins in the CSF from being trapped and interfering with the proper operation of the device. A feed pipe in the downstream chamber is provided to direct CSF flow through the orifice directly to the second pressure regulation valve when the differential pressure exceeds the aforementioned second threshold value.
The aforementioned arrangement of parts provides a simple and compact device and allows the threshold or popping pressure of the first pressure regulation valve and the closing or blow-out pressure of the flow regulation valve to be adjusted independently of each other. For example, at least one of the annular seats is formed in a screw threadedly received within a wall of the housing, allowing the screw be to be positioned axially within the housing to a predetermined extent. By adjusting the screws, the positions of the upstream and downstream annular seats can be varied to set the opening pressure at a first threshold value and the closing pressure at a second threshold value. The second pressure regulation valve may be provided as a slit valve disposed in an opening passing axially through the downstream seat which forms the opening through the downstream screw.
In another embodiment of the invention, the drainage device is provided with a housing having a cylindrical chamber therein in which a ball valve is positioned to move between first and second conical end seats. The inlet duct to the first pressure regulation valve opens out in the center of the first conical seat and the outlet duct from the flow regulation valve opens out at the center of the second conical seat. A calibration spring biases the ball in the direction of the first conical seat to prevent CSF flow through the chamber when the differential pressure across the device is below the popping pressure. Under increasing pressures, the ball valve will move toward the second conical end seat. A feed duct to a second pressure regulation valve opens out from the cylindrical chamber with the second pressure regulating valve positioned outside housing to direct CSF flow to a drainage location when the differential pressure exceeds a second threshold value.